#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>

int g_child_stop = 0;
int g_parent_run = 0;

void sig_child(int signum)
{
       	if( SIGUSR1 == signum )
	{
		g_child_stop = 1;
	}
}

void sig_parent(int signum)
{
	if( SIGUSR2 == signum )
	{
		g_parent_run = 1;
	}
}

int main(int argc, char **argv)
{
	int        pid;
	int        wstatus;
	signal(SIGUSR1, sig_child);
	signal(SIGUSR2, sig_parent);
   
	if( (pid=fork()) < 0 )
	{
		printf("Create child process failure: %s\n", strerror(errno));
		return -2;
	}
	else if(pid == 0)
	{
		/* child process can do something first here, then tell parent process to start running */
		printf("Child process start running and send parent a signal\n");
	       	kill(getppid(), SIGUSR2);

		while( !g_child_stop )
      		{
			sleep(1);
		}

		printf("Child process receive signal from parent and exit now\n");
		return 0;
	}
	printf("Parent hangs up untill receive signal from child!\n");
	while( !g_parent_run )
       	{
		sleep(1);
	}
	/* parent process can do something here, then tell child process to exit */
	printf("Parent start running now and send child a signal to exit\n");
	kill(pid, SIGUSR1);

	/* parent wait child process exit */
	wait(&wstatus);

	printf("Parent wait child process die and exit now\n");
	return 0;
}

